Electrical measuring instrument.



1 794.3951 19111313111111) JULY 11, 1905.

ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED JAN. 20,1904.

2 SHEBTSSHEET l.

WlT/VESSES: nvvE/vro/e ATTORNEY N0. 794.395. PATENTED JULY 11, 1905.

P. CONRAD.

ELECTRICAL MEASURING INSTRUMENT.

APPLIOATION FILED JAN. 20. 1904.

2 SHEETS-SHEET 2.

WITNESSES; cg IIVVENTOR -6%@% @H I y/ '1 c ATTORNEY UNITED STATESPatented July 11, 1905.

PATENT OFFICE.

FRANK CONRAD, OF EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSEELECTRIC & MANUFACTURING COMPANY, A COR- PORATION OF PENNSYLVANIA.

ELECTRICAL MEASURING INSTRUMENT.

SPECIFICATION forming part of Letters Patent No. 794,395, dated July 11,1905.

Application filed January 20, 1904- Serial No. 189,909.

To all whom it may concern.-

Be it known that I, FRANK CONRAD, a citizen of the United States, and aresident of Edgewood Park, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement in ElectricalMeasuring Instruments, of which the following is a specification.

rent or of its frequency of alternations and which shall be inherentlydead-beat.

Another object of myinvention is to provide an instrument which issimple, compact, and inexpensive in construction.

In the accompanying drawings, Figure 1 is a bottom plan view of aportable instrument constructed in accordance with my invention, onepair of the coils being shown in section. Fig. 2 is a diagrammatic viewof the connections and arrangements of the various circuits of theinstrument; and Fig. 3 is a sectional view on line III III of Fig. 1,also showing an inclosing case and a dial for the instrument.

The horseshoe-shaped iron core 1 of the instrument is provided withconcave-faced polepieces 2, having recesses 3, a cylindrical coreportion 4: being placed within the space between concave faces in orderto decrease the reluctance of the magnetic circuit. Theelectromagnetical portions of the instrument constitute practically aseries transformer in which the outer coils 5, that are here shown asconnected in series with the external circuit, form the primary windingand the inner coils 6 the secondary winding. The secondary winding isconnected in series with auxiliary coils 7, which surround portions ofthe pole-pieces that are reduced in cross-section by recesses 3, formedin the inner faces of the pole-pieces.

A hollow cylinder 8, which may be of the same material as the coils 7,surrounds the cylindrical portion a of the iron core and is supported bya shaft 9, which is provided with a pointer 10 and with suitableretarding means, such as a spring 11. The shaft 9 may also be providedwith an arm 12, which engages with a stop 13 to limit the movement ofthe rotating member. One of the jeweled bearings for the shaft issecured in the end of a screw 14, which projects into an opening 15 inthe cylindrical portion 4 of the iron core.

The instrument may be mounted upon the back of a slab 16, of marble orother suitable insulating material, which is provided with a graduateddial 17 and with a raised protecting crystal or cover 18, the wholebeing inclosed in a case 19, substantially as shown, for portable use.

. The action of the instrument may be understood from a consideration ofthe diagram of Fig. 2. When the current in the coils 5 is in thedirection indicated by the arrows 20, the magnetic flux produced by itin'the core is in the direction indicated by the arrow 21, and thecurrent induced in the coils 6 is in the direction indicated by thearrows 22. The arrows 23 indicate the directions of the currents in thecoils 7 and the arrows 24 the directions of the fluxes produced by thesecurrents. The resultant of the main flux produced by the coils 5 andthat produced by the coils 7 is a diagonal flux from the pole-face 25 topole-face 27, as indicated by the arrows 29. During a succeeding instantthe flux will assume a direction from the pole-face 26 to pole-face 28and will make one rotation during a complete period of alternation ofthe current. Currents are induced in the cylinder 8, and the rotaryfield exerts a dragging force upon these cur rents,causing the cylinderto rotate or exerting a torque upon said cylinder.

In order to obtain an instrument which will indicate accuratelyregardless of the frequency of alternations, the pull on the movablemember must be constant for a current corresponding to a givendeflection. The pull on the movable member or the torque tending toproduce rotation thereof is proportional to the product of the magneticfield, the ampereturns of the coils 7, and the frequency ofalternations. In a series transformer the main flux in the core isinversely proportional to the frequency with a constant secondary load,and the component of the primary current which produces thismagnetization is in the case of non-inductive load on the secondaryapproximately ninety degrees behind the main primary current. In myinstrument the load on the secondary consists practically of the ohmicresistance of the secondary coils 6 and that of the auxiliary coils 7,and therefore the conditions above described will obtain. Since the pullor torque on the rotatable member 8 is proportional to the productof themagnetic flux, frequency and current in the coils 7, the force exertedwith any given current remains constant for any frequency,'because achange of frequency will vary the main flux in the inverse ratio and thecurrent in the coils 7 is practically the same at all frequencies foragiven current in the coils 5, and hence the product of the threequantities remains constant. Any variation in the magnetizing componentof the primary current will have but slight effect on the resultantsecondary current, as this component is at right angles to the componentof the main current and also of much smaller value because of lowmagnetic reluctance and low voltage per turn.

My instrument is practically independent of temperature, since the coils7 are ordinarily of the same conducting material as the cylinder 8, andtherefore the resistances of the two increase at the same rate with riseof temperature. If the tem peratu re rises, the greater resistance ofthe coils 7 will require a higher voltage impressed on them to cause thesame current to How that previously flowed and hence a highermagnetization in the core, which will compensate for higher resistancein the movable member 8.

Since the cylindrical shell or movable member 8 rotates in a magneticfield, the instrument is inherently deadbeat, according to principleswell understood in the art.

Variation of wave form affects only the iron losses of electricalapparatus, and since these losses are Very small in my instrument it ispractically independent of wave form-.

I claim as my invention 1. An alternating-current electrical measuringinstrument comprising primary and securing instrument, the combinationwith a bipolar core and a conducting member rotatabl y mounted betweenthe pole-pieces of said core, of primary and secondary field-coils onsaid core, and auxiliary coils on the pole-pieces that are connected inseries with the secondary coils for producing magnetic fluxes whichoppose and displace the primary flux.

3. In an alternating-current electrical measuring instrument, thecombination with a bipolar core, primary and secondary field-coils, andauxiliary coils connected in series with the secondary coils and mountedin axial alinement therewith, of a rotatable, conducting member locatedbetween the pole-pieces of said core.

4:. In an alternating-current electrical measu ring instrument, thecombination with a bipolar core and a rotatable conducting memberbetween the pole-pieces thereof, of a pair of magnetizing-coils, a pairof secondary coils and a pair of auxiliary coils, said auxiliary coilsbeing connected in series with said secondary coils and so disposed onsaid polepieces as to produce a rotating field.

5. In an alternating-current electrical measuring instrument, thecombination with a core and a rotatable conducting member between thepole-pieces thereof, of magnetizing-coils and secondary coils thatsurround said core, and auxiliary coils that are connected in serieswith said secondary coils and also surround said core but are locatednearer to said rotatable member and are so disposed as to produce arotating field to act upon the rotatable cylinder.

6. An alternating-current electrical measuring instrument having a core,a rotatable conducting member between the pole-pieces of said core,coils for magnetizing said core, and means for producing a rotatingfield comprising secondary coils and auxiliary coils connected in seriestherewith and located in recesses in the pole-pieces.

7. In an alternating-current electrical measuring instrument, means forproducing rotation of the movable member comprising a bipolar core,primary and secondary coils that surround said core and auxiliary-coilsthat surround the pole-pieces of saidcore adjacent to the movable memberand are connected in series with the secondary coils.

8. An alternating-current measuring instrument comprising a magnetizablecore, primary and secondary field-coils that surround said core,auxiliary coils that surround the core pole-pieces and are connected inseries with the secondary coils, a conducting member rotatably mountedbetween said polepieces and means for indicating the degree or amount ofmovement of said rotatable member.

9. An alternating-current measuring instrument comprising a magnetizablecore, primary and secondary field-coils that surround said core,auxiliary coils that surround the core pole-pieces and are connected inseries with the secondary field-coils, a conducting member rotatablymounted between said polepieces, means for indicating the degree oramountof movementof said rotatable member and means for retarding orrestraining the movement of said member.

10. The combination w th a magnetizable core and a rotatable, conductingmember, of a primary exciting-winding, a secondary winding and anauxiliary winding that is connected in series with the secondary windingand that surrounds portions of the pole-pieces of the core.

11. The combination with a bipolar magnetlzable core and a rotatableconducting member, of a primary magnetizing-winding, a secondary windingand an auxiliary winding that is connected in circuit with the secondarywinding and that surrounds portions of the pole-pieces of the core.

In testimony whereof I have hereunto subscribed my name this 11th day ofJanuary, 1904.

FRANK CONRAD.

Witnesses:

J 0s. W. ALEXANDER, BIRNEY HINES.

